Traditionally, chromated deoxidizers have been used to enable aluminum samples to pass designated corrosion tests, as for example, MIL-C-5541C. The aluminum is first cleaned in a relatively non-etching alkaline soak cleaner, deoxidized in an acidic chromate solution and subsequently chromated. Alternatively, if etching was desired, an alkaline etch or alkaline chemical milling solution was used. This step was followed by a deoxidation step which usually employed a chromated deoxidizer, to remove "smut" produced by etching. The aluminum was then chromated. In the past, attempts to replace chromate in the deoxidizing step have generally involved the use of iron salts such as ferric sulfate. However, iron based deoxidizers have never provided results equal to the chromate containing deoxidizer systems.
U.S. Pat. No. 4,451,304 to Batiuk provides a treatment for aluminum which employs an alkaline cleaning step and a deoxidizer step. The deoxidizer step employs a non-chromate deoxidizer which is an aqueous solution of sodium or potassium nitrite. This patent, which is incorporated herein by reference, includes a detailed discussion of the prior art in this area.
Other than in the operating examples and claims, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about".